Scratchbuilding a Yellowstone.

[Jake S.]

Hey all! I've been lurking around here for a long time and I've finally decided that I should start posting. I'm currently designing an HO scale 2-8-8-4 in Autodesk Inventor. I'm hoping that I will be able to bring it into reality at some point in the future, and I am trying to design it in such a way that that will be possible, but only time will tell. I'm in way over my head with this as it is, and if I want to get anywhere I'm going to need some serious help. Here's some quick info about the project:

Locomotive type: 2-8-8-4 Yellowstone
Railroad: Ossic River Northern (My freelanced railroad, Class 1, runs west/northwest US in UP/SP/NP/WP territory, could conceivably be a proto-lanced replacement for WP and NP.)
Purpose: Slow hauling of long freights over steep (~2-3% grade) mountain passes.
Length: TBD
Driver Diameter: 63"
Builder: Lima Locomotive works or Baldwin Locomotive works. (Or maybe even both! While researching prototype Yellowstones I learned that NP Z-5s were built by both Baldwin and Alco!)
Notable/defining characteristics: flying pumps, Elesco feedwater heater, pilot mounted headlight, vestibule cab, centipede tender with doghouse.

Thus far I've managed to get some preliminary drawings done for the drivers. Here are some pictures:


Model for the 1st, 2nd, and 4th driver sets on each bogie. Small counterweight for just connecting rods.


Model for 3rd driver set on each bogie, larger counterweight for main rod and eccentric crank.


Driver profile view. Fully NMRA RP-25 compliant, code 88 instead of 110 for a slightly better look.

There are still a few issues with these, namely there is no real or viable provision for connecting to axles or rods yet, save for the pin you see, (which will obviously need to be changed) and a 1/16" diameter hole on the back. (Which will again, obviously need to be changed- the hole you see in the front of the driver is only cosmetic and about 2 scale inches in diameter.)

I'm 100% open to comments and criticism, like I said, I know I'm in way over my head and need plenty of help!

[peteski]

Wow!  That is a serious undertaking! Looks good so far.

The only comment I have at this time is to reduce your design down to 54%   

[Jake S.]

Quick update:

I changed a couple small things with the drivers. I removed the connecting rod pin and replaced it with a 0.05" diameter hole, and also upped the size of the axle hole to 0.1". Those sizes sound odd, but they will both allow me to have the wheels cast without issue by Shapeways (should I choose to... still not sure.) and then tap the holes to 1/16" and 1/8" myself. I also increased the width of the lobes that the side rods connect to to make clearance with the counterweights a bit less tight; it was 2 scale inches (0.023"), now it's 3 scale inches (0.035"). Lastly, I changed up the sizes of the 2nd and 4th axle counterweights. The original was an okay size for the leading axle, but the other two needed slightly larger counterweights based on prototype photos.

Here's a pic of the gang all together. I'm quite happy with them and will probably start work on the connecting rods soon, but I'm always open to c&c.